The trapping of mobile carriers, i.e., electrons and holes, reduces the peak current, maximum operating frequency, microwave power, and efficiency of a semiconductor device. In many semiconductor devices, particularly in those made of wide bandgap materials such as gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), indium phosphide (InP), and/or the like, mobile carrier trapping occurs due to the presence of various types of defects. Mobile carrier trapping can occur in the bulk of the material as well as at the device surface. Trapping occurring at the device surface is important in lateral devices, such as field effect transistors (FETs) having an active channel located close to the device surface.
Noise and interference are related issues that can affect the performance of a semiconductor device. Such noise and interference can be caused by a surface potential modulation occurring due to noise sources, industrial equipment, power lines, etc.
FIGS. 1A and 1B show illustrative heterostructure field effect transistors (HFETs) 2A and 2B, respectively, according to the prior art. In the HFET 2A, the active heterostructure is passivated using a passivation layer included over the gate G and covering an entire spacing between the source S and drain D. In the HFET 2B, a field plate electrically connected to the gate G is also included above the passivation layer. Various alternative configurations are possible. For example, an HFET can include several field plates connected to different electrodes. In each case, the surface element(s) are included to alleviate mobile carrier trapping and/or noise and interference.